Atomic structure, radiation, collisions: what s in it for

YR, ICTP/IAEA School, 2019

Atomic structure, radiation, collisions:

what’s in it for plasmas?..Yuri Ralchenko

National Institute of Standards and Technology

Gaithersburg, MD 20899, USA


plasma

t=0

The story of a photon


Questions to ask

• Why was the photon created?

• Who created the photon?

• What was the probability for the photon to be created?

• How does the plasma environment affect photon creation?

• How did the photon propagate in the plasma?

• What has changed when the photon was recorded?

• ……………


ൻΨ𝑓 𝑎′, 𝑏′, 𝑐′, . . . Ο ۧΨ𝑖 𝑎, 𝑏, 𝑐, . . .

initial statefinal stateinteractionoperator

Most of the relevant physics is inside this matrix element

Why is atomic structure important for plasmas?

• Wavelengths• Energies• Transition probabilities (radiative and non-radiative)• Collisional cross sections• …


A Few Textbooks on APP● H.R. Griem

– Plasma Spectroscopy (1964)

– Principles of Plasma Spectroscopy (1997)

● R.D. Cowan

– Theory of Atomic Structure and Spectra (1981)

● V.P. Shevelko and L.A. Vainshtein

– Atomic Physics for Hot Plasmas (1993)

● D. Salzmann

– Atomic Physics in Hot Plasmas (1998)

• T. Fujimoto• Plasma Spectroscopy (2004)

• H.-J. Kunze• Introduction to Plasma

Spectroscopy (2009)

• J. Bauche, C. Bauche-Arnoult, O. Peyrusse• Atomic Properties in Hot

Plasmas (2015)

• Modern Methods in Collisional-Radiative Modeling of Plasmas (2016)• HKC, CJF, YR,…


Units

• Energy• 1 Ry = 13.61 eV = 109 737 cm-1 (ionization energy of H)

• 1 eV = 8065.5447 cm-1

• Length• a0 = 5.2910-9 cm = 0.529 Å (radius of H atom)

• Area (cross section)• a0

2 = 8.8 10-17 cm2 (area of H atom)

• New SI (redefinition of base units): May 20 2019

http://physics.nist.gov/cuu/Units/


What kind of atomic data is of importance for spectroscopic diagnostics of plasmas?

• Wavelengths of spectral lines

• Line/level identifications

• Level energies

• Transition probabilities (radiative and non-radiative processes)

• Collisional cross sections and rate coefficients

• Spectral line shapes and widths


16-electron ion (S-like): how to describe its atomic structure?..

8

Averageatom

122836

1224344452

12283541

Superconfiguration

3s23p34s

3s23p3d24p

Configuration 5S

3S

3D

1D

3P

1P

LS term

3D1

3D2

3D3

Level


Hydrogen and H-like ions

Hydrogen atom H-like ion

Radius:

Energy:

1 R

y =

13

.61 e

V

𝑎𝑛 ~𝑛2

𝒁

𝐸𝑛 = −𝒁𝟐𝑅𝑦

𝑛2


Each atomic state (wavefunction) is characterized by a set of quantum numbers

• Generally speaking, only two are exact for an isolated atom:• Total angular momentum J

• Parity = −1 σ𝑖 𝑙𝑖 (but: weak interactions!)

• They are the consequences of conservation laws• Noether theorem (1915)

• Everything else (total L, total S,…) is not exact!


Complex atoms (non-relativistic)

𝐻 = 𝐻𝑘𝑖𝑛 + 𝐻𝑒𝑙𝑒𝑐−𝑛𝑢𝑐𝑙 + 𝐻𝑒𝑙𝑒𝑐−𝑒𝑙𝑒𝑐 + 𝐻𝑠−𝑜 + …

= −

𝑖

1

2𝛻𝑖2 −

𝑖

𝑍

𝑟𝑖+

𝑖>𝑗

1

𝑟𝑖𝑗+

𝑖

1

2𝜉𝑖 𝑟𝑖 𝒍𝒊 ∙ 𝒔𝒊 + …

The Schrödinger equation for multi-electron atoms cannot be solved exactly…

𝐻Ψ 𝒓1, 𝒓2, … = 𝐸Ψ 𝒓1, 𝒓2, …

We know all important interactions:


Standard procedure• Use central-field approximation to approximate the effects of the

Coulomb repulsion among the electrons:

• 𝐻 ≈ 𝐻0 = σ𝑖𝑁 −

1

2𝛻𝑖2 −

𝑍

𝑟𝑖+ 𝑉 𝑟𝑖

• Properly choose the potential V(r)

• Find configuration state functions Φ 𝛾𝑗𝐿𝑆 (accounting also for antisymmetry): n,l

• Assume that the atomic state function is a linear combination of CSFs: Ψ 𝛾𝐿𝑆 = σ𝑗

𝑀 𝑐𝑗Φ 𝛾𝑗𝐿𝑆

• Solve Schrodinger equation for mixing coefficients:

• 𝐻 − 𝐸 መ𝐼 Ƹ𝑐 = 0, 𝐻𝑖𝑗 = Φ 𝛾𝑖𝐿𝑆 𝐻 Φ 𝛾𝑗𝐿𝑆

• Include other effects (perturbation theory)…and live happily!


Relativistic atomic structure: heavy and not so heavy ions

𝐻𝐷𝐶 =

𝑖

𝑐 𝜶𝑖 ∙ 𝒑𝑖 + 𝑉𝑛𝑢𝑐 𝑟𝑖 + 𝛽𝑖𝑐2 +

𝑖>𝑗

1

𝑟𝑖𝑗

𝒑 ≡ −𝑖𝜵 electron momentum operator

𝜶, 𝛽 4x4 Dirac matrices

Dirac-CoulombHamiltonian

𝐻𝑇𝑃 = −

𝑗>𝑖

𝛼𝑖 ∙ 𝛼𝑗 𝑐𝑜𝑠 𝜔𝑖𝑗𝑟𝑖𝑗/𝑐

𝑟𝑖𝑗+ 𝜶𝑖 ∙ 𝜵𝑖 𝜶𝑗 ∙ 𝜵𝑗

𝑐𝑜𝑠 𝜔𝑖𝑗𝑟𝑖𝑗/𝑐 − 1

𝜔𝑖𝑗2 𝑟𝑖𝑗/𝑐

2

𝑉𝑛𝑢𝑐 𝑟 extended nuclear charge distribution

Transverse photons (magnetic interactions and retardation effects):

QED effects: self energy (SE), vacuum polarization (VP)

𝐻𝐷𝐶𝐵+𝑄𝐸𝐷 = 𝐻𝐷𝐶 +𝐻𝑇𝑃 + 𝐻𝑆𝐸 +𝐻𝑉𝑃


Relativistic notations

s1/2 p1/2 p3/2 d3/2 d5/2 f5/2 f7/2

s p- p+ d- d+ f- f+

l 0 1 1 2 2 3 3

j ½ ½ 3/2 3/2 5/2 5/2 7/2

𝑙± → 𝑗 = 𝑙 ± 1/2


Energy structure of an ion

Electrons are grouped into shells nl(K n=1, L n=2, M n=3,...)producing configurations (or even superconfigurations)

~Z2

~Z ~Z4

termslevels

electron-nucleusinteraction

electron-electroninteraction

spin-orbit(relativistic effects)

Every state is defined by a set ofquantum numbers which are mostlyapproximate

Continuum

Boundstates


Z-scaling of electron energies

𝐸0 = −1

𝑛2

𝐻 =

𝑖

𝑝𝑖2

2−𝑍

𝑟𝑖+

𝑖>𝑗

1

𝑟𝑖𝑗

New variables 𝜌𝑖 = 𝑍𝑟𝑖 , 𝑝𝑖 = 𝑝𝑖/𝑍 lead to:

𝐻 = 𝑍2

𝑖

𝑝𝑖2

2−1

𝜌𝑖+ 𝑍

𝑖>𝑗

1

𝜌𝑖𝑗= 𝑍2 𝐻0 + 𝑍−1𝑉

Kinetic+nuclear

electrons

𝐻𝜓 = 𝐸𝜓 ⇒ 𝐻0 + 𝑍−1𝑉 𝜓 = 𝑍−2𝐸 𝜓

𝐸 = 𝑍2 𝐸0 + 𝑍−1𝐸1 + 𝑍−2𝐸2 +⋯

Therefore, for high Z the energy structure looks more and more H-like!


Mg-like Al II: 3l3l'

Ionization potential

2p63s2

Grotrian diagram


Mg-like Sr XXVII: 3l3l'

Ionization potential

2p63s2


Importance of Zc

Spectroscopic charge: Zc= ion charge + 1 (H I, Ar XV…)

This is the charge that is seen by the outermost (valence) electron

Isoelectronic sequences: ions with the same number of electrons• Li I, Be II, B III,…

It is often useful to consider variation of atomic parameters along isoelectronic sequences


Spin-orbit interaction

Hydrogenic ion: 𝜁𝑛𝑙 =𝑅𝑦 𝛼2 𝑍4

𝑛3 𝑙 𝑙 + 1/2 𝑙 + 1

Semi-theoretical Lande formula: 𝜁𝑛𝑙 =𝑅𝑦 𝛼2 𝑍𝑐

2 ෨𝑍2

𝑛∗3 𝑙 𝑙 + 1/2 𝑙 + 1

n*: effective n 𝐼 =𝑅𝑦 𝑍𝑐

2

𝑛∗2

෨𝑍: effective nuclear charge (for penetrating orbits) = Z-n for np orbitals

𝐻 = −

𝑖

1

2𝛻𝑖2 −

𝑖

𝑍

𝑟𝑖+

𝑖>𝑗

1

𝑟𝑖𝑗+

𝑖

1

2𝜉𝑖 𝑟𝑖 𝒍𝒊 ∙ 𝒔𝒊 + …


Types of coupling

• LS coupling: electron-electron » spin-orbit• light elements

• jj coupling: spin-orbit » electron-electron• heavy elements

• 2s2p: (2s1/2,2p1/2) or (2s,2p-)

• 3d5: ((3d-3)5/2,(3d+

2)2)3/2

• Intermediate coupling: neither is overwhelmingly strong

• Other types of couplings exist

𝐿 = Ԧ𝑙1 + Ԧ𝑙2+. . . , Ԧ𝑆 = Ԧ𝑠1 + Ԧ𝑠2+. . . , Ԧ𝐽 = 𝐿 + Ԧ𝑆

Ԧ𝑗1 = Ԧ𝑙1 + Ԧ𝑠1, Ԧ𝑗2 = Ԧ𝑙2 + Ԧ𝑠2, . . . Ԧ𝐽 = Ԧ𝑗1 + Ԧ𝑗2+. . .


sp

1P

3P

1P1

3P2

3P1

3P0

terms levels states

M

+1-1 0

0-1+1

-2

+2

electro-static

spin-orbit

magneticfield

+1-1 0

0

+G1

-G1

Configuration sp: LS coupling (LSJ)


sp

(1/2,3/2)

terms levels states

M

+1-1 0

0-1+1

-2

+2

spin-orbit

electro-static

magneticfield

+1-1

0

0

Configuration sp: jj coupling

(1/2,1/2)

(1/2,3/2)1

(1/2,3/2)2

(1/2,1/2)1

(1/2,1/2)0


From LS to jj: 1s2p in He-like ions

1P1


Spin-orbit interaction does depend on nuclear charge!

Landeformula

𝜁𝑛𝑙 =𝑅𝑦 𝛼2 𝑍𝑐

2 ෨𝑍2

𝑛∗3 𝑙 𝑙 + 1/2 𝑙 + 1


Na-like doublet: from neutral to HCI

D1

D2

5890 Å

5896 Å

0.1%

Fraunhofer absorption linesin the solar spectrum

D1: 3s1/2 – 3p1/2

D2: 3s1/2 – 3p3/2


D1

D2

5890 Å

5896 Å

0.1%3p3/2

3p1/2

Na-like doublet: from neutral to HCI


Sodium Atom (Na0+)

Sodium-like Tungsten (W63+)

Little Ions With a Big Charge

11 electrons


D-doublet in Na-like W, Hf, Ta, and Au

J.D. Gillaspy et al,

Phys. Rev. A 80,

010501 (2009)


State mixing in intermediate coupling

expansion coefficients

He-like Na9+: 1s2p 3P1

= 0.999 3P + 0.032 1PHe-like Fe24+: 1s2p 3P

1= 0.960 3P + 0.281 1P

He-like Mo40+: 1s2p 3P1

= 0.874 3P + 0.486 1P

Ψ 𝑎, 𝑏, 𝑐, . . .= 𝛼 ⋅ Ψ1 𝑎, 𝑏, 𝑐, . . . + 𝛽 ⋅ Ψ2 𝑎, 𝑏, 𝑐, . . . + 𝛾 ⋅ Ψ3 𝑎, 𝑏, 𝑐, . . . +. . .

Very, VERY important for radiative transitions!!!


Hund’s rules (equivalent electrons, LS)• Largest S has the lowest

energy

• Largest L with the same Shas the lowest energy

• For atoms with less-than half-filled shells, lowest Jhas lowest energy

C I

O I


SuperconfigurationsMotivation: for very complex atoms (ions) not only the number of levels isoverwhelmingly large, but also the number of configurations

Example: 1s22s22p53s1s22s22p53p1s22s22p53d1s22s2p63s1s22s2p63p1s22s2p63d

(1s)2(2s2p)7(3s3p3d)1 ≡ (1)2(2)7(3)1

different n’s

BUT: (1s)2(2s2p)7(3s3p3d4s4p4d4f)1

Instead of producing millions or billions of lines, SCs are used to calculate Super Transition Arrays

Statistical methods

See J. Bauche et al’s book (2015)


Superconfigurations vs.detailed level accounting

Ga: photoabsorptioncross section

Iglesias et al (1995)


Ionization potentials• IPs are directly connected with ionization

distributions in plasmas

• Most often are determined from Rydberg series

1 10 10010

100

1000

10000

Ioniz

atio

n p

ote

ntia

l (e

V)

Spectroscopic charge, Zsp=z+1

IP

A + B*Zc + C*Z2c

Ne-like ions: 1s22s22p6

experiment

int/ext

theory


Ionization potentials of W ions

Closed-shell ions exist for wideranges of plasma temperatures

𝑍2𝑅𝑦 = 74505 𝑒𝑉

𝐼 𝑊73+ = 80756 𝑒𝑉


Ionization potential: constant?..

• IP is a function of plasma conditions

• High-lying states are no longer bound due to interactions with neighboring atoms, ions, and electrons

• Orbit radius in H I: where is n=300,000?


-4 -3 -2 -1 0 1 2 3 4-15

-10

-5

0

Energ

y (

eV

)

X

n=1

n=2

n=3n=4

−1

𝑋

continuum

Isolated atom


-4 -3 -2 -1 0 1 2 3 4-15

-10

-5

0

Energ

y (

eV

)

X

unbound

QM tunneling

Ionizationpotential

depression

Stewart-Pyatt: ∆𝐼 ≈ 2.2 ∙ 10−7𝑧

𝑟𝑖1 +

𝑟𝑑

𝑟𝑖

3 2/3

−𝑟𝑑

𝑟𝑖

2(eV)


Atomic Structure Methods and Codes● Coulomb approximation (Bates-Damgaard)

● Thomas-Fermi (SUPERSTRUCTURE, AUTOSTRUCTURE)

● Single-configuration Hartree-Fock (self-consistent field)

– Cowan’s code (LANL)

● Model potential (including relativistic)

– HULLAC, FAC

● Multiconfiguration non-relativistic HF (http://nlte.nist.gov/MCHF)

● Multiconfiguration Dirac-(Hartree)-Fock (MCDF or MCDHF)

– GRASP2K (http://nlte.nist.gov/MCHF)

– Desclaux’s code

● Various perturbation theory methods (MBPT, RMBPT)

● B-splines

http://plasma-gate.weizmann.ac.il/directories/free-software/


Atomic Structure & Spectra Databases

• (Reasonably) Extensive list • http://plasma-gate.weizmann.ac.il/directories/databases/

• Evaluated and recommended data• NIST Atomic Spectra Database http://physics.nist.gov/asd

• Level energies, ionization potentials, spectral lines, transition probabilities

• Other data collections• VALD (Sweden)• SPECTR-W3 (Russia)• CAMDB (China)• CHIANTI (USA/UK/…)• Kurucz databases (USA)• GENIE (IAEA)• …


Now to radiative processes…


Three major sources of photons

• Free-free transitions (bremsstrahlung)• Az+ + e → Az+ + e + hν

• Free-bound transitions (radiative recombination)• Az+ + e → A(z-1)+ + hν

• Bound-bound transitions• Aj

z+ → Aiz+ + hν

Ener

gy

Continuum

Bound states

A

B

C

Ionizationenergy


●Bremsstrahlung (free-free)

• Calculation is straightforward for Maxwellian electrons off bare nuclei of Z:

• Total power loss

• Multicomponent plasma:

+

E1

E2

( )( )

( )

,1

33

322

2/1

2

3

0e

ffT

hc

e

eZ

ff TGeT

RyZNN

Ryace

−

=

= −

3

2/1

2451051.4cmsr

WNN

Ry

TZ ez

eff

Dominant at longer wavelengths

( ) ( )

===

zi

i

zi

zi

i

zi

zi

i

zi

e

eff

ff

eff

ff

Nz

NzNz

NzHz

,

,

2

,

21;

Maximum emission at eVT

nm

e

620max =


Bremsstrahlung (cont’d)

𝜀 𝜆 𝑑𝜆 = 𝜀 𝜔 𝑑𝜔 𝜔 =2𝜋𝑐

𝜆

( )( )

( )

,33

642/1

2

3

0e

ffT

e

eZ

ff TGeT

RyZNN

c

Ryace

−

=

𝜀𝜔𝑓𝑓

𝐸 ≈ 𝐴𝑒−𝐸𝑇𝑒


Spectral Line Intensity

Einstein coefficient ortransition probability (s-1)

Upper state density (cm-3)

Photon energy (erg)Energy emitted due to a specifictransition from a unit volumeper unit time

(almost) purelyatomic parametersstrongly depends

on plasma conditions ijijjij EANI =


BB Radiative transitions

● Classical rate of loss of energy: dE/dt ~ |a|2, and decay rate ~ |r|2 for harmonic oscillator

● Quantum treatment:

– eikr = 1+ikr+… 1 (electric dipole or E1 = allowed)

– Velocity form:

– Length form:

i

rki

f ea

if

if r

must be equal foran exact wavefunction(good test!)


Why would a STATIONARY excited state of the atomic Hamiltonian not live forever but rather experience a radiative decay to a lower state?..

QUESTION:


S, f, and A (1)

• Line strength • Symmetric w/r to initial-final

• Oscillator strength (absorption or emission)• gjfij = gifji (gj = 2Jj+1); dimensionless

• Typical values for strong lines: ~ 0.1-1

j

iijji SjriS ==

2

SRy

E

gf

i

ij

=

3

1


S, f, and A (2)

• Transition probability (or Einstein coefficient)

• Typical values for neutrals: ~108-109 s-1

j

i

( ) ][103.4 127 −= sfeVEg

gA ij

j

iji

ijijijjiji BgBgBc

hA == ,

22

3

Lifetime: j=1/ΣiAji

H I: 4.7e8 (1-2)5.6e7 (1-3)

He I: 1.8e9 (1s2-1s2p)5.7e8 (1s2-1s3p)


Selection rules and Z-scaling

Fundamental law: parity and J do not change

Before:

After:

jj JP

phiphi JJPP

+

Exact selection rules:Pj = - Pi

|J| ≤ 1, 0 → 0 (Jj+Ji1)

Pph = -1Jph(E1) = 1

Approximate selection rules (for LS coupling):S = 0, |L| ≤ 1, 0 → 0

Intercombination transitions: S ≠ 02s2 1S0 – 2s2p 3P1


Selection rules and Z-scaling

•n ≠ 0• r Z-1 S Z-2

• E Z2 f Z0

•A Z4

•n = 0• r Z-1 S Z-2

• E Z f Z-1

•A Z

ijji SjriS ==2


Some useful info

• “Left” is stronger than “right”• f(l = -1) > f(l = +1)

• He I• f(1s2p 1P1 – 1s3s 1S0) = 0.049

• f(1s2p 1P1 – 1s3d 1D2) = 0.71

• Level grouping• Average over initial states

• Sum over final states

• Example: from levels to terms

• Any physical parameter

sp

d

p

j

i

A

B

=

i

j

j

j

ijj

BAg

g


Principal quantum number n

• n-dependence for f:

• n-dependence for A

• Total radiative rate from a specific n

( )

( )

( )3

2

12

3

2

5

1

3

2

2

2

1

21

1

245.033

41

1111

33

32

nnnf

nnnf

nnnnnnf

=

−→

−

( )2/9

410106.1

n

ZnAZ

( )3

2

12

1

nnnA


Mixing effects

He-like Na9+: 1s2p 3P1

= 0.999 3P + 0.032 1PHe-like Fe24+: 1s2p 3P

1= 0.960 3P + 0.281 1P

He-like Mo40+: 1s2p 3P1

= 0.874 3P + 0.486 1P

Z 1s2 1S0 - 1s2p 1P1 1s2 1S0 - 1s2p 3P1

2 1.8(9) 1.8(2)

11 1.3(13) 1.4(10)

26 4.6(14) 4.4(13)

42 2.6(15) 9.0(14)

54 6.7(15) 3.0(15)

74 2.2(16) 1.2(16)


Quick estimates of A

( ) ][103.4 127 −= sfeVEg

gA ij

j

iji

Calculate A(Fe24+ 1s2 1S0 - 1s2p 1P1) if f(O6+ 1s2 1S0 - 1s2p 1P1) = 0.7

NIST ASD: 4.6·1014 s-1 (<10%)


Forbidden transitions (high multipoles)

• QED: En, Mn (n=1, 2,…)

• E1/M1 dipole, E2/M2 quadrupole, E3/M3 octupole,…

• Selection rules• PjPi

• +1 for M1, E2, M3,…• -1 for E1, M2, E3,…

• Jph(En/Mn) = n

• M3 and E3 were measured!

• Magnetic dipole (M1)• Stronger within the same

configuration/term

• A Z6 or stronger

• Same parity, |J| ≤ 1, Jj+Ji1

• Electric quadrupole (E2)• Stronger between

configurations/terms

• A Z6 or stronger

• Same parity, |J| ≤ 2, Jj+Ji2

Generally weak…


Aurora borealis


Forbidden transitions: auroras

O I 2p4

3P

1D

1S E2: 5577 ÅM1: 6300 ÅM1: 6364 Å

Wavelength Transition A(s-1)

2958 1S0-3P2 E2: 2.42(-4)

2972 1S0-3P1 M1: 7.54(-2)

5577 1S0-1D2 E2: 1.26(+0)

6300 1D2-3P2 M1: 5.63(-3)

6300 1D2-3P2 E2: 2.11(-5)

6364 1D2-3P1 M1: 1.82(-3)

6364 1D2-3P1 E2: 3.39(-6)

6392 1D2-3P0 E2: 8.60(-7)


Scaling in Ne-like ions

Jönsson et al, 2011


Forbidden transitions: highly-charged W

W52+

W52+

W52+

W51+

W53+

W53+

W51+

Practically all strong lines are due to M1 transitionswithin 3dn ground configurations

EBIT spectrum: EB = 5500 eV

A ~ 104-106 s-1


He-like Ar Levels and Lines

1s2 1S0

1s2s 1S0

1s2p 1P1

1s2s 3S1

1s2p 3P0

1s2p 3P1

1s2p 3P2

W

X

YZ

E1

2E1

Line He0 Ar16+ Fe25+ Kr34+

W 1.8(9) 1.1(14) 4.6(14) 1.5(15)

Y 1.8(2) 1.8(12) 4.4(13) 3.9(14)

X 3.3(-1) 3.1(8) 6.5(9) 9.3(10)

Z 1.3(-4) 4.8(6) 2.1(8) 5.8(9)


Z-scaling of A’s

• W[E1]: A(1s2 1S0 – 1s2p 1P1) Z4

• ΔJ = 1, P1*P2 = -1, ΔS = 0

• Y[E1]: A(1s2 1S0 – 1s2p 3P1)• ΔJ = 1, P1*P2 = -1, ΔS = 1

• Z10 for low Z

• Z8 for large Z

• Z4 for very large Z

• X[M2]: A(1s2 1S0 – 1s2p 3P2) Z8

• ΔJ = 2, P1*P2 = -1, ΔS = 1

• Z[M1]: A(1s2 1S0 – 1s2s 3S1) Z10

• ΔJ = 1, P1*P2 = -1, ΔS = 1


j

i

t ~ 1/A

Why are the forbidden lines sensitive to density?


Radiative Recombination

AZ+ + e → A(Z-1) + hh = E + I

E

I

Semiclassical Kramers cross section: ( ) 2

0

3

5

4

33

64a

IE

Ry

n

ZEKr

+=

Quantummechanical cross section: ( ) ( ) ( )EGEE bf

nKrph =

Cross section Z-scaling:

22

1

ZZ

h

(inverse of photoionization)


FF+BF at Alcator C-mod: 1 eV, H

Edge: n=1

n=2

n=3

Lumma et al (1997)


Collisions in plasmas

• More than one particle: collisions!

• Elastic, inelastic

projectile_density[1/cm3] *velocity[cm/s] *effective_area[cm2]

Number of collisions per unit time:

v

Equilibrium plasma: Te = TA

𝑣𝑒𝑣𝐴

=𝑀

𝑚𝑒

Electrons are much faster!

[1/s]


Collision (excitation)

e

ΔE

ΔE

.

..

Continuum

Atom

Main binary quantity: cross section (E) [cm2]

Effective area for a particular process

Process rate in plasmas:

𝑅[𝑠−1] = 𝑁 𝜎v ≡ 𝑁 න

𝐸𝑚𝑖𝑛

𝐸𝑚𝑎𝑥

𝜎 𝐸 ⋅ v ⋅ 𝑓 𝐸 𝑑𝐸

𝜎 𝐸 = න 𝑓 𝐸, 𝜃, 𝜙2

𝑑Ω

rate coefficient

f is the scattering amplitude

Physics is here!


Basic Parameters

● Cross sections are probabilities

– Classically:

● Typical values for atomic cross sections

– a0 ~ 5·10-9 cm a02 ~ 10-16 cm2

● Collision strength Ω (dimensionless, on the order of unity):

– Ratio of cross section to the de Broglie wavelength squared

– Symmetric w/r to initial and final states

𝜎 Δ𝐸, 𝐸 = න

0

∞

𝑃 Δ𝐸, 𝐸, 𝜌 ⋅ 2𝜋𝜌𝑑𝜌

𝜎𝑖𝑗 𝐸 = 𝜋𝑎02𝑅𝑦

𝑔𝑗𝐸Ω𝑖𝑗 𝐸

ρ

v


Direct and inverse

• Quantum mechanics tells us that characteristics of direct and inverse processes are related

excitation

deexcitation

Ω𝑖𝑗 𝐸 + Δ𝐸 = Ω𝑗𝑖 𝐸

i

j

𝑔𝑖 𝐸 + Δ𝐸 𝜎𝑒𝑥𝑐 𝐸 + Δ𝐸 = 𝑔𝑗𝐸𝜎𝑑𝑥𝑐 𝐸

ΔE is the excitation threshold

𝑔𝑖 𝜎𝑣 𝑒𝑥𝑐 = 𝑔𝑗 𝜎𝑣 𝑑𝑥𝑐 ∙ 𝑒−Δ𝐸/𝑇

Klein-Rosseland formula:

Milne formula for photoionization/photorecombination: ℏ𝜔 = 𝐸 + 𝐼𝑍

𝑔𝑧𝜎𝑝ℎ ℏ𝜔 =2𝑚𝑐2

ℏ2𝜔2𝑔𝑧+1𝜎𝑟𝑟 𝐸𝐴 + ℎ𝜈 ↔ 𝐴+ + 𝑒

𝐴 𝑖 + 𝑒 ↔ 𝐴 𝑗 + 𝑒 Rates:


Types of transitions for excitation

● Optically(dipole)-allowed

– P·P' = -1 (different parity)

– |∆l| = 1

– ∆S = 0

– (E→∞) ~ ln(E)/E

● Optically(dipole)-forbidden

– ∆S = 0

– (E→∞) ~ 1/E

● Spin-forbidden (EXCHANGE! Coulomb does not change spin…)

– ∆S ≠ 0

– (E→∞) ~ 1/E3

Examples in He I:

1s2 1S → 1s2p 1P

1s2p 3P → 1s4d 3D

1s2s 1S → 1s3s 1S

1s2s 3S → 1s4d 3D

1s2 1S → 1s2p 3P

1s2p 3P → 1s4d 1D


Order of cross sections● General order

– optically allowed > optically forbidden > spin forbidden

● OA: long-distance, similar to E1 radiative transitions

● The larger Δl, the smaller cross section

Li-like ions: 2s – 2p excitation

Excitation cross sections for ions are NOTzero at the threshold

+e-


From cross sections to rates

v𝜎 = න

𝐸𝑚𝑖𝑛

𝐸𝑚𝑎𝑥

v ⋅ 𝜎 𝐸 ⋅ 𝑓 𝐸 𝑑𝐸𝑀𝑎𝑥𝑤 8

𝜋𝑚𝑇3

1/2

න

Δ𝐸

∞

𝐸 ⋅ 𝜎 𝐸 ⋅ 𝑒−𝐸/𝑇𝑑𝐸

For (E) = A/E: 𝑣𝜎 ∝𝑒−

Δ𝐸𝑇

𝑇

Rate coefficients for an arbitrary energy distribution function

Often only threshold is important:

𝛾 𝑇𝑒 =1

𝑇𝑒නΩ 𝐸 exp −

𝐸

𝑇𝑒𝑑𝐸

𝑅𝑗𝑖 𝑇𝑒

=8

𝜋𝑚𝑇𝑒

1/2𝜋𝑎0

2

𝑔𝑖𝑅𝑦 ⋅ 𝛾𝑗𝑖 𝑇𝑒

Effective collision strength:


van Regemorter-Seaton-Bethe formula

● Optically-allowed excitationsGaunt factor

oscillatorstrength

X≡E/ΔEij𝜎𝑖𝑗 𝐸 = 𝜋𝑎0

28𝜋

3

𝑅𝑦

Δ𝐸𝑖𝑗

2𝑔 𝑋

𝑋𝑓𝑖𝑗

𝑋 → ∞ : 𝑔 𝑋 ≈3

2𝜋ln 𝑋 𝜎 𝐸 ≈

6.51 ⋅ 10−14

Δ𝐸 𝑒𝑉 2

ln( 𝑋)

𝑋𝑓𝑖𝑗 𝑐𝑚−2

“Recommended” Gaunt factors:

𝑔 Δ𝑛 = 0, 𝑋 = 0.33 −0.3

𝑋+0.08

𝑋2ln 𝑋

𝑔 Δ𝑛 ≠ 0, 𝑋 =3

2𝜋−0.18

𝑋ln 𝑋

Atoms:

𝑔 Δ𝑛 = 0, 𝑋 = 1 −1

𝑍0.7 +

1

𝑛0.6 +

3

2𝜋ln 𝑋

𝑔 Δ𝑛 ≠ 0, 𝑋 = 0.2 𝑋 < 2 ,3

2𝜋ln 𝑋 𝑓𝑜𝑟 𝑋 ≥ 2

Ions:


Scaling of Excitations

𝜎𝑖𝑗 𝐸 ∝𝑓

Δ𝐸𝑖𝑗2

• n-scaling• n=1

• f~n, E~n-3, ~ n7, ~ n4

• Into high n

• f~n-3, E~n0, ~ n-3

• Z-scaling• n=0

• f~Z-1, E~Z, ~ Z-3, <σv> ~ Z-2

• n≠0

• f~Z0, E~Z2, ~ Z-4, <σv> ~ Z-3


Direct and Exchange (cont’d)

1s2

1s2p

2s2

2s2p

Ne IX

Ne VII

He-like ion Be-like ion


Ionization cross sections

Z

Lotz formula:

𝜎𝑖𝑜𝑛 𝑛, 𝐸 = 2.76 𝜋𝑎02𝑅𝑦2

𝐼𝑛

ln 𝐸/𝐼𝑛𝐸

= 2.76 𝜋𝑎02𝑛4

𝑍4ln 𝑋

𝑋

Same theoretical methods as for excitation: Born, Coulomb-Born, DW, CC, CCC, RMPS…

𝐴 + 𝑒 → 𝐴+ + 𝑒 + 𝑒


3-Body Recombination

𝐴 + 𝑒 ↔ 𝐴+ + 𝑒 + 𝑒

3-body rate coefficient 𝛼𝑍+1 𝑇𝑒 from ionization rate coefficient 𝑆𝑍 𝑇𝑒 :

𝛼𝑍+1 𝑇𝑒 =1

2

𝑔𝑧𝑔𝑧+1

2𝜋ℏ2

𝑚𝑒𝑇𝑒

3/2

𝑒𝑥𝑝𝐸𝑧𝑇𝑒

𝑆𝑍 𝑇𝑒

Rates from rate coefficients: 𝑛𝑒𝑆𝑍 𝑇𝑒 but 𝑛𝑒2𝛼𝑍+1 𝑇𝑒

Likes high-n states; 𝛼 𝑇𝑒 ~1/𝑇𝑒9/2


Collisional Methods and Codes● Plane-wave Born (first order perturbation)

● Coulomb-Born (better for HCI)

● Distorted-wave methods

● Close-coupling (CC) methods

– Convergent CC (CCC)

– R-matrix (with pseudostates, etc.)

– B-splines R-matrix

– Time-Dependent CC

– …

● Relativistic versions are available


Heavy-particle collisions

In thermal plasmas electrons are always more important for excitations than heavy particlesException: closely-spaced levels (e.g., 2s and 2p in H-like ions)

Neutral beams: E ~ 100-500 keV heavy particle collisions are of highest importance

Charge exchange H + Az+ H+ + A(z-1)+(n) • Very large cross sections > 10-15 cm2; 𝜎 𝑍 ~𝑍 ∙ 10−15 𝑐𝑚2

• High excited states populated: 𝑛 ~ 𝑍0.77

• Higher l values are preferentially populated but it depends on collision energy and n

Ionization cross sections


Neutral beam in ITER: H+W64+

Classical Trajectory Monte Carlo (CTMC): two variations

D.R.Schultz and YR, to be published

𝜎 𝑍 ~𝑍 ∙ 10−15 𝑐𝑚2 = 𝟔. 𝟒 ∙ 𝟏𝟎−𝟏𝟒 𝑐𝑚2 𝑛 ~ 𝑍0.77 ≈ 𝟐𝟓


Autoionization

1s2 1s2l 2l2l’

IP~ ¾ IP

Energy of 2l2l’

∆E

∆E

A** → A+ + e

𝐴𝑎 =2𝜋

ℏ𝜓 𝐻 𝜑

2; 1013-1014 s-1


Resonances in excitation

e e e

Direct excitation Intermediate states Intermediate AI states(coupled channels!)


Excitation-Autoionization

3s23p63d104s2 Xe24+: Pindzola et al, 20113p63d Ti3+: van Zoest et al, 2004

IP

When EA is important:• few electrons on the outermost shell• Mid-Z multielectron ions• …but less important for higher Z (rad!)

EA in ionization cross sections isnot required for detailed modelingwith AI states!


Resonances in photoionization

A. Pradhan

Fe III

3d5(6S)ns 7S + hν-> 3d5 6S

3d5(6S)ns 7S + hν-> 3d44p(4Po)ns 7Po

-> 3d5 6S


Selection rules

• Examples of AI states: 1s2s2, 1s22pnl (high n)

• Same old rule: before = after

• A** →A* + l• Exact: Pj = Pi; J = 0• Approximate (LS coupling): S = 0, L = 0

• 2p2 3P → 1s + p: parity/L violation (for LS)!

• BUT: (2p2 3P2 ) = (2p2 3P2 ) + (2p2 1D2) + …• and (2p2 3P0 ) = (2p2 3P0 ) + (2p2 1S0) + …• YET: Aa(2p2 3P1) is much smaller…


2p2 autoionization probabilities

Level Ne8+ Fe24+

3P0 2.2(10) 3.7(12)3P1 3.1(8) 1.9(10)3P2 6.2(11) 1.1(14)1D2 2.7(14) 2.3(14)1S0 1.4(13) 3.2(13)


Radiative recombination

Continuum

Bound states

𝐴 𝑍+1 + + 𝑒 → 𝐴𝑍+ + ℎ𝜈

Ion recombined


DR step 1: dielectronic capture

Continuum

Bound states

Resonant process!

𝐴 𝑍+1 + + 𝑒 → 𝐴𝑍+∗∗


Continuum

Bound states

𝐴 𝑍+1 + + 𝑒 → 𝐴𝑍+∗∗ → 𝐴 𝑍+1 + + 𝑒

Dielectronic capture + autoionization= no recombination

DC and AI aredirect and inverse


DR step 2: radiative stabilization

Continuum

Bound states

𝐴 𝑍+1 + + 𝑒 → 𝐴𝑍+∗∗ → 𝐴𝑍+∗ + ℎ𝜈

Stabilizing transition:Mostly x-rays


Dielectronic Recombination

A++e → A** → A++eDC AI

A*+h

Example: Δn=0 for Fe XX 2s22p3

2s22p3 4S3/2 + e → 2s2p4(4P5/2)nl2s22p3 4S3/2 + e → 2s2p4(4P5/2)nl2s22p3 4S3/2 + e → 2s2p4(4P5/2)nl

RS

Savin et al, 2004

n ≥ 7


Examples of dielectronic recombination & resonances

A. Burgess, ApJ 139, 776 (1964)

This work solved the ionization balance problem for solar corona

He+ + e

Ar at NSTX, Bitter et al (2004)

Dielectronic satellites areimportant for plasma diagnostics

(e.g., He- and Li-like ions)

BUT: DR for high-Z multi-electron ionsis barely known!


Connection between DC and EXC

∆E

∆E

∆E

∆E

∆E

∆E

∆E

∆E

?


Connection between DC and EXC

∆E

∆E

DC can be treated asan under-threshold excitationand DC cross sections can bederived by extrapolation ofthe excitation cross sections


Inner-shell dielectronicresonances in HCI

𝐾2𝐿8𝑀𝑘 + 𝑒 → 𝐾2𝐿7𝑀𝑘𝑛𝑙𝑛′𝑙′

~Yb40+


Experiment

LMnLNn

5

67

4

5

6

Theory

1s22s22p63s23pm3dk + e → 1s22s22p53s23pm3dk+1nl

1s22s22p63s23pm3dk + e → 1s22s22p53s23pm3dk4lnl'

1s22s22p63s23pm3dk + e → 1s22s2p53s23pm3dk+1nl


He-like lines and satellites

O.Marchuk et al, J Phys B 40, 4403 (2007)


Energy levels in He-like Ar

• Ground state: 1s2 1S0

• Two subsystems of terms• Singlets 1snl 1L, J=l (example 1s3d 1D2)

• Triplets 1snl 3L, J=l-1,l,l+1 (example 1s2p 3P0,1,2)

• Radiative transitions within each subsystem are strong, between systems depend on Z


He-like Ar Levels and Lines

1s2 1S0

1s2s 1S0

1s2p 1P1

1s2s 3S1

1s2p 3P0

1s2p 3P1

1s2p 3P2

W

X

YZ

E1

2E1

Line He0 Ar16+ Fe25+ Kr34+

W 1.8(9) 1.1(14) 4.6(14) 1.5(15)

Y 1.8(2) 1.8(12) 4.4(13) 3.9(14)

X 3.3(-1) 3.1(8) 6.5(9) 9.3(10)

Z 1.3(-4) 4.8(6) 2.1(8) 5.8(9)


Z-scaling of A’s

• W[E1]: A(1s2 1S0 – 1s2p 1P1) Z4

• Y[E1]: A(1s2 1S0 – 1s2p 3P1) • Z10 for low Z

• Z8 for large Z

• Z4 for very large Z

• X[M2]: A(1s2 1S0 – 1s2p 3P2) Z8

• Z[M1]: A(1s2 1S0 – 1s2s 3S1) Z10


1s2lnl satellites

• 1l2l2l’• 1s2s2: 2S1/2

• 1s2s2p:• 1s2s2p(1P) 2P1/2,3/2

• 1s2s2p(3P) 2P1/2,3/2; 4P1/2,3/2,5/2

• 1s2p2

• 1s2p2(1D) 2D3/2,5/2

• 1s2p2(3P) 2P1/2,3/2; 4P1/2,3/2,5/2

• 1s2p2(1S) 2S1/2

• 1s2lnl’• Closer and closer to W• Only 1s2l3l can be reliably resolved• Contribute to W line profile

1s2+𝑒 ↔ 1𝑠2𝑙2𝑙′

Documents

Atomic structure, radiation, collisions: what s in it for